Catheter ablation is a method to treat arrhythmia by inserting an ablation catheter into the heart chamber and cauterizing the cardiac muscle tissue with an electrode attached to the anterior end of the catheter.
A recently developed balloon ablation catheter is used by percutaneously introducing a balloon attached to the anterior end side of the catheter into the inferior vena cava and then delivering it via the right atrium and then the interatrial septum of the heart to the left atrium, where the balloon is inflated and heated with high-frequency power to cauterize the cardiac muscle tissue (JP 2002-78809 A and JP 4062935 B). This catheter has now become the mainstream in catheter ablation.
In the use of a balloon ablation catheter, a balloon attached to the anterior end of the catheter is inflated with a heating liquid, and a high-frequency current is applied between a counter electrode plate outside the body of the patient and a high-frequency-current-applying electrode arranged inside the balloon, to heat the heating liquid. The whole cardiac muscle tissue that is in contact with the balloon surface is thus cauterized. The temperature of the balloon surface is controlled by a temperature sensor arranged inside the balloon, and the heating liquid inside the balloon is made uniform by stirring with an oscillator or the like.
A thermocouple temperature sensor in which a metal wire that supplies high-frequency power to the high-frequency-current-applying electrode is point-bonded to a different type of metal wire is often used as the temperature sensor for the balloon ablation catheter. It is said that in such a case, arrangement of the thermocouple near the posterior end of, and on the surface of, the high-frequency-current-applying electrode allows secure positioning of the thermocouple inside the balloon, leading to increased reliability of the detected temperature (JP 4226040 B). However, at the same time, since the thermocouple temperature sensor is positioned near the lumen that communicates with the inside of the balloon, the sensor is likely to be directly influenced by cooling with the heating liquid discharged for stirring into the balloon so that there is a problem of instability of control of the balloon surface temperature.
On the other hand, to suppress the influence of cooling with the heating liquid discharged into the balloon, an attempt has been made to arrange the thermocouple temperature sensor in the anterior end portion of the high-frequency-current-applying electrode (JP 4222152 B).
However, if the thermocouple temperature sensor is arranged in the anterior end side of the high-frequency-current-applying electrode, the different type of metal wire needs to be further extended to the anterior end side in the balloon. In this case, the flexibility of the catheter in the portion where the different type of metal wire is extended is deteriorated, and the balloon diameter upon contraction near the high-frequency-current-applying electrode increases, resulting in difficulty in introducing the balloon ablation catheter into the body of the patient and disadvantages in terms of operation of the catheter and the burden on the patient.
Further, wherever the thermocouple temperature sensor is arranged on the surface of the high-frequency-current-applying electrode, point bonding of the different type of metal wire needs secure adhesion by soldering or the like, and this adhesion is one of the factors that increase the balloon diameter upon balloon contraction. Further, since the strength of the thermocouple prepared by point bonding of the different type of metal wire cannot be fully reliable, development of measures to suppress the risk of wire breakage and the like is an urgent task, and improvement of reliability of the thermocouple temperature sensor has been demanded.
It could therefore be helpful to provide a balloon ablation catheter that achieves reduction in the diameter of the balloon upon balloon contraction and increased reliability of the thermocouple temperature sensor, which balloon ablation catheter is less likely to be influenced by the heating liquid discharged into the balloon and able to control the balloon surface temperature with high accuracy.